Air Conditioner Troubleshooting (Guide)

airconditioner troubleshooting

Is your air conditioner giving you trouble? It might be an easy fix, or it could need professional repair; in either case, it helps to get acquainted with how your AC unit works.

In this guide, the team at Same Day Pros will help you learn more about how AC units work and some methods for troubleshooting problems you might encounter so you can better prepare your AC repair technician when they arrive.

How Air Conditioning Units Work

Every air conditioning unit functions a little differently and is built for different purposes. The basic principles of how it works, however, stays the same. (1) Contrary to popular belief, air conditioning units remove the warm air from inside your home or room and pump it outside.

“Contrary to popular belief, air conditioning does not literally blow cool air inside—it takes the warmer air away.”

If you’ve ever been in a building with central air conditioning, you’ll notice that the area around the outdoor unit is hotter than everywhere else. This is because the outdoor unit is releasing the hot air from inside the home.

Once the air conditioning unit takes in warm air, this flows over pipes that cool the air and remove excess moisture. The coolant inside the pipes turns into a warm gas as it cools down the air, then flows into the condenser which returns it to a cooled liquid state to cycle. Excess heat is pumped outside.

The air, which has now been cooled, is then cycled back into the home at a much lower temperature.

The introduction of this cooler, less humid air lowers the overall temperature and humidity of the room or home as it pumps more warm air into the unit to be cooled.

Central Air Conditioning Unit

A central air conditioning unit is a large unit in the home that is meant to cool the entire home, rather than a few rooms. This is achieved through ductwork that spans each room in the home.

A thermostat somewhere in the home controls the temperature the system uses to guide how often it comes on, and for how long.

Inside the interior unit, coils filled with coolant dehumidify and chill the air that is drawn into the unit, while a filter removes particles and allergens from the air to keep it breathable. A blower fan disperses the chilled air into the air vents, which then travels to individual rooms in the home.

Traveling between this unit and the outside is a copper coil which coolant travels along to enter an exterior unit. This exterior unit houses a fan, condenser coils, and compressor to release excess heat and help cool the coolant down again as it re-enters the system.

Window or Portable AC Unit

portable ac

Window AC units and portable AC units work similarly to a central AC system, except the unit is more compact to save on space.

While a central air system cannot be moved once installed, these two types of units can be removed in preparation for colder months. Both portable and window units require access to a window to pump the hot air outside.

Typically, the thermostat is on the front of the unit and in newer models, can be controlled by the use of a remote. As temperatures rise above the thermostat’s range, the unit will activate the blowers, which pumps cool air into the room after it has been cooled inside.

The coils still need to release excess heat, but without a separate exterior unit.

In window units, this exterior unit is the back of the system which hangs out the exterior of the window. This portion of the unit contains the condenser which cools the coils back down and pumps the hot air outside.

In portable units, a hose must be attached to the back of the unit, which is then secured to the window with specialized panels. The hot air is released into the hose, where it rises and escapes through the opening out of the window.

Air Conditioner Troubleshooting: What Your HVAC Tech Will Look For First

ac troubleshooting

While individual technicians’ processes will vary depending on the problem they’ve been called in for, they will check for certain problems during routine maintenance.

How well the unit is functioning, as well as how clean it is, can tell the technician a story about how the unit has been treated. How the unit looks will also give the technician clues about potential problems it may have or be susceptible to.

Below are some of the most common checks that HVAC technicians look for when inspecting your unit.

Changed Thermostat Settings

One of the first things that a technician will look at is how the unit responds to changed thermostat settings. They will also inspect the thermostat for other issues, such as sensor issues or faulty electrical connections.

If a thermostat is set to a temperature far above the current temperature, the unit may struggle to reach that temperature; the thermostat should be set no more than 5-8 degrees below the current temperature and adjusted from there.

If changing the thermostat does not activate the AC unit despite everything being turned on, a reset may be necessary, or it could be a problem with the unit’s sensors.

Refrigerant Leaks

Refrigerant leaks are not common but can be an issue if part of the line has been damaged or punctured. Leaking refrigerant can not only pose a hazard if it is leaking inside the home, but it can also lessen the efficiency of your unit as it is unable to cool the air down as much.

Refrigerant, also called coolant, is critical to keeping your air cold and the unit operating safely. Leaks should be handled by a professional HVAC technician as soon as possible.

Inadequate Maintenance

Even if your AC unit seems to be doing fine, regular maintenance can benefit the system as it ensures everything is properly cleaned and well-maintained for the next time it is used. This is especially important for areas that only require the unit for infrequent or seasonal use, as the system will be idle for many months at a time.

Maintaining the unit also ensures that the belts, blower fans, and coils are all in good shape, as they can wear out over time with frequent or improper use.

Making proactive repairs ahead of time will keep your unit running when you need it most, extending the overall lifespan of the unit and the efficiency of the cooling system.

Failing to maintain the unit properly can result in expensive cooling costs, inefficiency cooling, and untimely malfunctions.

Dirty Air Filters

Dirty air filters can affect any unit, but most commonly central air units. (2) Dirty air filters are easy to replace on your own and do not require an HVAC technician to do yourself unless the unit is tucked away in a place that is difficult to reach.

“filters should be cleaned every two to four weeks. To clean the filter, remove the front panel of the unit. If a reusable filter is in place, vacuum it to remove as much dirt as possible.”

To replace or clean your air filter, there should be a labeled door on the front of the unit. Opening this door typically requires unscrewing a bolt or screw first, as this helps keep the filter in place. Open the door and take the filter out, either disposing of it or vacuuming it if it is reusable.

Replace the filter with the correct side up – which should be labeled on the filter – firmly into the unit. It should not wiggle or be loose in the unit when replaced. Once done, close the door and replace the bolt on the door.

Electric Control Failure

Almost every AC unit requires electricity to run, and an electric control failure can prevent it from performing certain checks or turning on at all. Whether your unit is a larger central air system or a portable or window unit, it can suffer from electric control failure within the unit itself.

This problem can appear with a variety of symptoms, and you may notice the unit functioning incorrectly. If this occurs, it is important to contact your HVAC technician and turn the unit off to prevent further damage.

DIY fixes are not recommended as the problem can be difficult to diagnose and dealing with the electrical systems inside the unit can be unsafe if handled incorrectly. If the unit is repaired incorrectly, it can cause further damage to the unit and pose a safety hazard during normal usage.

Sensor Problems

An AC unit relies on sensors that help it identify when to turn on and off, as well as how hot or cold the air in the home is. The sensor may be faulty, displaced, or lack power.

If you have a central thermostat that tells a separate unit when to run, but it does not seem to be communicating with the other unit, you may have a power issue on hand and can easily be fixed by replacing the batteries inside the thermostat. This should resume communication between the sensor and unit.

A displaced sensor, either in a separate thermostat or in a single unit can cause problems as the sensor will lose accuracy in telling the temperature and may have problems communicating with the unit. This should be addressed by a professional as it can be difficult to repair on your own.

If the unit has a faulty thermostat, either as a separate unit or within a single unit, it can cause the unit to short-cycle intermittently, wearing on the unit’s lifespan and causing difficulty in reaching the desired temperature. This should be addressed by a professional as it can be difficult to diagnose and repair on your own.

Drainage Problems

In any AC unit, the drain line is a critical piece of equipment that allows the removed humidity to exit the unit and home. In most units, there is a drip pan that allows this water to collect in case the line is backed up.

If there is water standing in the drip pan, the line is clogged and should be drained. Typically, this happens because dust or dirt particles make their way into the unit over time, and this residue can build up as it is carried along inside the unit, as the drain line is one of the only exits from the unit.

Cleaning the drain line can be difficult or require specialized equipment, making it unsuitable for DIY fixes, so it is important to have the work done by a certified and experienced HVAC technician.

Common Air Conditioning Problems

Air conditioner troubleshooting is a hot topic, and to cool things down it’s necessary to know some of the common problems that might be affecting the unit.

Below are some of the most common air conditioning problems that occur that might send you on a Same Day Pros search for a technician near you.

AC Short Cycling – Won’t Stop Running

Short-cycling is when the unit turns off, only to turn on again in quick succession. This is not good for the unit, and not healthy for your utility bill. (3)

all that cycling on and off can stress the equipment and shorten its life span.

Short-cycling may also be a sign of another problem with the unit, which should be addressed by an HVAC technician. To prevent further damage to the unit, turn it off while waiting for a technician, even if it is supplying a little bit of cold air to the home.

AC Doesn’t Turn On

If your AC unit doesn’t turn on at all, it may be a problem with the thermostat or an electrical connection to the unit. If you have a central home thermostat, replacing the batteries is a good step towards troubleshooting the problem. It may also help to reset the AC unit.

If this does not solve the problem, you should consult with your local HVAC technician for further air conditioner troubleshooting.

If the unit has not seen a maintenance visit in a while, it may be activating a failsafe to prevent the unit from turning on while a line is clogged, or a critical part may be burnt out, requiring these parts are replaced or repaired before the unit can operate properly.

Unit Only Blows Hot Air

If the unit is blowing hot air, it may not be properly cycling the air through the cooling coils, or something may be wrong with the condenser if it is not returning coolant to the coils in the first place. This should be addressed by a technician as soon as possible, and the unit turned off to prevent further damage.

Why Is My Air Conditioner Running But Not Cooling the House?

If your air conditioning is running but isn’t cooling your house, it could be frozen. It sounds counterintuitive, but if there is too much coolant or a blockage in the line somewhere, your unit can freeze over, causing it to overheat in other areas as it continues to run. The unit should be turned off to prevent further damage.

If your unit is new, there is a chance that it is not large enough to cool the entire space and should either be upgraded or used with another source of cooling in the room. In air conditioning, size is everything; too small will struggle to cool the house, while too big will leave the house cold and clammy as it cannot remove enough moisture from the air before cooling it down.

How Do You Reset an Air Conditioning Unit?

Resetting an AC unit can take time, and depending on the type of unit, the steps may vary.

For window and portable units, simply turn off the AC if the thermostat is on and unplug it from the electrical outlet. The unit will take a few minutes to reset internally. Once the unit has rested, plug it back in and turn the unit back on at the thermostat interface.

For other types of AC units like central air, first, turn off the AC unit at the thermostat. Since you can’t simply unplug it, you’ll need to locate the AC on your circuit breaker. Switch this to the OFF position and let your AC rest.

Once the unit has rested, flip the circuit breaker switch back to the ON position, and turn the AC back on at the thermostat. Your air conditioning unit should reset.

How Long Does it Take an AC Unit to Reset?

In total, window and portable units typically take between 10-15 minutes to reset properly before being plugged back into the electrical outlet.

Central air conditioning units are a little more complicated and require more time to rest while being reset. These larger units should be allowed to rest for anywhere between 30 minutes and one hour.

If you are uncertain how long to let your unit rest between resetting, you should consult with your regular HVAC company, as they will be more familiar with the type and brand of your unit.

Should I Turn Off My AC If It Is Not Cooling?

Yes, you should always turn off your air conditioning unit if it is not cooling, malfunctioning, or in need of repair. Leaving the unit running can cause further problems, especially if it is having trouble cooling down at the end of the cycle.

If there is a malfunction in the cooling process or an electrical connection to the unit, it is critical to turn off the unit if you notice something isn’t right with it, as this can prevent safety hazards like fires.

Beyond safety concerns, leaving a unit running when it needs repair can be costly as the unit will run continuously, struggling to keep up with the thermostat’s demands with little efficiency. Your electricity bill will reflect this.

Furthermore, a frozen unit requires time to thaw before a technician can look at it, so even if your AC is only cooling a little bit, it should still be turned off so that the technician can go begin repairs immediately once they arrive; thawing out an AC unit can take hours, adding to repair costs.

When to Call an Expert to Repair Your AC Unit?

expert ac repair

Contrary to popular belief, a repair technician doesn’t have to be expensive. Proper maintenance and timely repairs can help extend the lifespan of your AC unit, no matter the type of system you have in your home.

All it takes is partnering with a professional who can work with you regularly, so it’s important to find someone you can trust. You don’t have to make all the repairs yourself, and getting in over your head with HVAC repairs can lead to further damage of the unit and potential safety hazards, so it is always recommended to work with a professional rather than trying DIY methods.

Are you in need of an HVAC technician to help you troubleshoot and repair your air conditioning unit? Just need someone to ask questions of when purchasing a new system? Looking for a maintenance service?

At Same Day Pros, we have everything you need, at your fingertips. Use our services today to find a licensed and insured HVAC expert who is available in your area.


  1., What is an HVAC System and How Does It Work?,
  2., 10 DIY Appliance Maintenance Tips to Keep Them Running Like New,
  3., The Best Way to Cool Your Space,

Leave a Reply

Your email address will not be published. Required fields are marked *